1. Field of the Invention
The present invention relates to an internal combustion engine with a cam phase change mechanism capable of changing the phase of an intake cam.
2. Description of the Related Art
Conventionally, there are internal combustion engines that comprise a cam phase change mechanism as a variable valve gear, which changes the phase of an intake cam to vary the opening and closing timings of an intake valve. Further, a technique has been developed in which the cam phase change mechanism is applied to internal combustion engines that are provided with a plurality of intake valves for each cylinder. According to this technique, the opening and closing timings of only some of the intake valves are varied in accordance with the engine load and speed.
In one such internal combustion engine, the opening and closing timings of the specific intake valves are delayed by the cam phase change mechanism, based on the operating state of the engine, whereby the open periods of the specific intake valves, along with those of ones not subject to delay control, can be extended (Jpn. Pat. Appln. KOKAI Publication No. 3-202602).
In the internal combustion engine described in the above patent document, vane-type cam phase change mechanisms formed of vane-type actuators have become widely used to make valve trains compact. Due to structural restrictions, however, these vane-type cam phase change mechanisms cannot easily produce great phase differences. Accordingly, the opening and closing timings of the intake valves cannot be substantially changed, so that it is difficult to considerably mitigate pumping loss by greatly extending the valve-open period.